1. Field of the Invention
The present invention relates to a multifilamentary oxide superconducting wire having an excellent superconducting property, and a method of efficiently obtaining such a multifilamentary oxide superconducting wire.
2. Description of the Related Art
Recently, Bi--Sr--Ca--Cu--O--, Y--Ba--Cu--O--, and Tl--Ba--Ca--Cu--O-based oxide superconductors whose critical temperatures exceed the temperature of liquid nitrogen are found, and studies on a variety of their applications are being made in various fields.
These oxide superconductors are brittle. Hence, to form them into oxide superconducting wires having predetermined shapes, for example, a raw material of an oxide superconductor is filled in a metal pipe to form a composite billet, and the composite billet is subjected to a diameter reduction process to obtain a desired shape. When a predetermined heating process is performed, the raw material is reacted to form an oxide superconductor, thereby obtaining a singlefilamentary oxide superconducting wire.
A multifilamentary oxide superconducting wire is manufactured in the following manner. That is, a multiple of oxide superconducting wires described above are arranged in a metal pipe, subjected to a diameter reduction process to obtain a desired shape, and subjected to a predetermined heating process. Alternatively, a plurality of through holes are formed in a metal billet, the raw material described above is filled in the through holes to form a composite billet, and the composite billet is subjected to a diameter reduction process to obtain a desired shape, and subjected to a predetermined heating process.
However, these methods provide either a multifilamentary oxide superconducting wire in which oxide superconductor filaments 11 each having a circular section are dispersed and composed in a metal matrix 10, as shown in FIG. 1A, or a multifilamentary oxide superconducting wire in which oxide superconductor filaments 12 each having a flat rectangular section are aligned in a predetermined direction and composed in a metal matrix 10, as shown in FIG. 1B.
The former cannot obtain a high superconducting property since the packing density of the oxide superconductor filaments 11 is low and the degree of c-axis orientation of the superconductor is low. In the latter, since the oxide superconductor filaments 12 each having the flat rectangular section are aligned only in the predetermined direction, the oxide superconductor filaments 12 become barriers against thermal conduction interfering with thermal conduction in the direction of thickness. As a result, the cooling capability of the multifilamentary oxide superconductor as a whole is decreased, and high superconducting property (such as critical temperature, critical current) cannot be obtained.
In the method of arranging multiple singlefilamentary oxide superconducting wires in the metal pipe, moreover it is difficult to align the singlefilamentary oxide superconducting wires in the metal pipe, and some oxide superconductor filaments inevitably intersect with each other in the obtained oxide superconductor. Since the intersecting portion is abnormally deformed, a high superconducting property cannot be obtained.
The method of forming a plurality of through holes in the metal billet is not preferable since the hole forming operation requires much labor, especially when the number of holes is large.